Phasic Store-Operated Ca2+ Entry During Excitation-Contraction Coupling in Skeletal Muscle Fibers From Exercised Mice

Store-operated calcium entry (SOCE) plays a pivotal role in skeletal muscle physiology as, when impaired, the muscle is prone to early fatigue and the development of different myopathies. A chronic mode of slow SOCE activation is carried by stromal interaction molecule 1 (STIM1) and calcium-release activated channel 1 (ORAI1) proteins. A phasic mode of fast SOCE (pSOCE) occurs upon single muscle twitches in synchrony with excitation-contraction coupling, presumably activated by a local and transient depletion at the terminal cisternae of the sarcoplasmic reticulum Ca2+-stores. Both SOCE mechanisms are poorly understood. In particular, pSOCE has not been described in detail because the conditions required for its detection in mouse skeletal muscle have not been established to date. Here we report the first measurements of pSOCE in mouse extensor digitorum longus muscle fibers using electrical field stimulation (EFS) in a skinned fiber preparation. We show moderate voluntary wheel running to be a prerequisite to render muscle fibers reasonably susceptible for EFS, and thereby define an experimental paradigm to measure pSOCE in mouse muscle. Continuous monitoring of the physical activity of mice housed in cages equipped with running wheels revealed an optimal training period of 5-6 days, whereby best responsiveness to EFS negatively correlated with running distance and speed. A comparison of pSOCE kinetic data in mouse with those previously derived from rat muscle demonstrated very similar properties and suggests the existence and similar function of pSOCE across mammalian species. The new technique presented herein enables future experiments with genetically modified mouse models to define the molecular entities, presumably STIM1 and ORAI1, and the physiological role of pSOCE in health and under conditions of disease.

Endogenous Chemerin from PVAT Amplifies Electrical Field-Stimulated Arterial Contraction: Use of the Chemerin Knockout Rat

Background: We previously reported that the adipokine chemerin, when added exogenously to the isolated rat mesenteric artery, amplified electrical field-stimulated (EFS) contraction. The Chemerin1 antagonist CCX832 alone inhibited EFS-induced contraction in tissues with but not without perivascular adipose tissue (PVAT). These data suggested indirectly that chemerin itself, presumably from the PVAT, facilitated EFS-induced contraction. We created the chemerin KO rat and now test the focused hypothesis that endogenous chemerin amplifies EFS-induced arterial contraction. Methods: The superior mesenteric artery +PVAT from global chemerin WT and KO female rats, with endothelium and sympathetic nerve intact, were mounted into isolated tissue baths for isometric and EFS-induced contraction. Results: CCX832 reduced EFS (2-20 Hz)-induced contraction in tissues from the WT but not KO rats. Consistent with this finding, the magnitude of EFS-induced contraction was lower in the tissues from the KO vs. WT rats, yet the maximum response to the adrenergic stimulus PE was not different among all tissues. Conclusion: These studies support that endogenous chemerin modifies sympathetic nerve-mediated contraction through Chemerin1, an important finding relative in understanding chemerin's role in control of blood pressure.

Urethral dysfunction in a rat model of chemically induced prostatic inflammation: potential involvement of the MRP5 pump

Prostate inflammation (PI) is a clinical condition associated with infection and/or inflammation of the prostate. It is a common disease frequently associated to lower urinary tract (LUT) symptoms. The urethra is an understudied structure in the LUT and plays a fundamental role in the urinary cycle. Here, we proposed to evaluate the effect of PI on the urethra tissue. Male Sprague-Dawley rats were used, and PI was induced by formalin injection into the ventral lobes of the prostate. The pelvic urethra at the prostatic level was harvested for histological analysis, contraction (electrical field stimulation and phenylephrine), and relaxation (sodium nitroprusside/MK-571) experiments. Various gene targets [cytochrome c oxidase subunit 2, transforming growth factor-β₁, interleukin-1β, hypoxia-inducible factor-1α, α_1A-adrenoceptor, inositol 1,4,5-trisphosphate receptor type 1, voltage-gated Ca²⁺ channel subunit-α_1D, neuronal nitric oxide synthase, soluble guanylyl cyclase, phosphodiesterase 5A, protein kinase CGMP-dependent 1, and multidrug resistance-associated protein 5 (MRP5; ATP-binding cassette subfamily C member 5)] were quantified, and cGMP levels were measured. No histological changes were detected, and functional assays revealed decreased contraction and increased relaxation of urethras from the PI group. The addition of MK-571 to functional assays increased urethral relaxation. Genes associated with inflammation were upregulated in urethras from the PI group, such as cytochrome oxidase c subunit 2, transforming growth factor-β₁, interleukin-1β, and hypoxia-inducible factor-1α. We also found increased expression of L-type Ca²⁺ channels and the neuronal nitric oxide synthase enzyme and decreased expression of the MRP5 pump. Finally, cGMP production was enhanced in urethral tissue of PI animals. The results indicate that PI is associated with proinflammatory gene expression in the urethra without histologically evident inflammation and that PI produces a dysfunctional urethra and MRP5 pump downregulation, which results in cGMP accumulation inside the cell. These findings would help to better understand LUT dysfunctions associated with PI and the role of MRP pumps in the control of LUT function.

Effects of epoxygenases on the nonadrenergic noncholinergic relaxant responses induced by electrical field stimulation in rabbit corpus cavernosum

We aimed to investigate the effects of epoxygenases on electrical field stimulation (EFS)-mediated nitric oxide (NO)-dependent and NO-independent nonadrenergic noncholinergic (NANC) relaxations in isolated rabbit corpus cavernosum. The tissues of 20 male adult albino rabbits (2.5-3 kg) were suspended in organ baths containing aerated Krebs solution, and isometric contractions were recorded. EFS-mediated NANC relaxations were obtained on phenylephrin (3 × 10^-5  M)-contracted tissues in the presence of guanethidine (10^-6  M) and atropine (10^-6  M). Miconazole (10^-9 -10^-4  M), 17-octadecynoic acid (ODYA) (10^-10 -10^-5  M), 14,15-epoxyeicosatrienoic acid (EET) (10^-11 -10^-8  M), 11,12-EET (10^-12 -3 × 10^-8  M) and 20-hydroxyeicosatetraenoic acid (HETE) (10^-11 -3 × 10^-8  M) were added cumulatively (n = 5-7 for each set of experiments). For NO-independent relaxations, N^ω -nitro-l-arginine methyl ester (l-NAME) (10^-4  M) was added before a group of experiments. Depending on the concentration, miconazole, 17-ODYA, 14,15-EET, 11,12-EET, and 20-HETE significantly enhanced both NO-dependent and NO-independent EFS-mediated relaxations (p < 0.05). Epoxygenases showed similar effect on NO-dependent and NO-independent relaxant responses except 20-HETE which caused significantly more enhanced relaxation on NO-dependent responses (p < 0.05). No drug caused a significant relaxation response on tissues contracted with phenylephrine. Epoxygenases contribute to EFS-mediated NO-dependent and NO-independent NANC relaxations by presynaptic mechanisms, offering a new treatment alternative for erectile dysfunction which needs to be explored in further in vivo, molecular and clinical studies.

Maintenance of contractile function of isolated airway smooth muscle after cryopreservation

Isolated human airway smooth muscle (ASM) tissue contractility studies are essential for understanding the role of ASM in respiratory disease, but limited availability and cost render storage options necessary for optimal use. However, to our knowledge, no comprehensive study of cryopreservation protocols for isolated ASM has been performed to date. We tested several cryostorage protocols on equine trachealis ASM using different cryostorage media [1.8 M dimethyl sulfoxide and fetal bovine serum (FBS) or Krebs-Henseleit (KH)] and different degrees of dissection (with or without epithelium and connective tissues attached) before storage. We measured methacholine (MCh), histamine, and isoproterenol (Iso) dose-responses and electrical field stimulation (EFS) and MCh force-velocity curves. We confirmed our findings in human trachealis ASM stored undissected in FBS. Maximal stress response to MCh was decreased more in dissected than undissected equine tissues. EFS force was decreased in all equine but not in human cryostored tissues. Furthermore, in human cryostored tissues, EFS maximal shortening velocity was decreased, and Iso response was potentiated after cryostorage. Overnight incubation with 0.5 or 10% FBS did not recover contractility in the equine tissues but potentiated Iso response. Overnight incubation with 10% FBS in human tissues showed maximal stress recovery and maintenance of other contractile parameters. ASM tissues can be cryostored while maintaining most contractile function. We propose an optimal protocol for cryostorage of ASM as undissected tissues in FBS or KH solution followed by dissection of the ASM bundles and a 24-h incubation with 10% FBS before mechanics measurements.

Early electrical field stimulation prevents the loss of spinal cord anterior horn motoneurons and muscle atrophy following spinal cord injury

Our previous study revealed that early application of electrical field stimulation (EFS) with the anode at the lesion and the cathode distal to the lesion reduced injury potential, inhibited secondary injury and was neuroprotective in the dorsal corticospinal tract after spinal cord injury (SCI). The objective of this study was to further evaluate the effect of EFS on protection of anterior horn motoneurons and their target musculature after SCI and its mechanism. Rats were randomized into three equal groups. The EFS group received EFS for 30 minutes immediately after injury at T₁₀. SCI group rats were only subjected to SCI and sham group rats were only subjected to laminectomy. Luxol fast blue staining demonstrated that spinal cord tissue in the injury center was better protected; cross-sectional area and perimeter of injured tissue were significantly smaller in the EFS group than in the SCI group. Immunofluorescence and transmission electron microscopy showed that the number of spinal cord anterior horn motoneurons was greater and the number of abnormal neurons reduced in the EFS group compared with the SCI group. Wet weight and cross-sectional area of vastus lateralis muscles were smaller in the SCI group to in the sham group. However, EFS improved muscle atrophy and behavioral examination showed that EFS significantly increased the angle in the inclined plane test and Tarlov's motor grading score. The above results confirm that early EFS can effectively impede spinal cord anterior horn motoneuron loss, promote motor function recovery and reduce muscle atrophy in rats after SCI.

Characterisation of Nav1.7 functional expression in rat dorsal root ganglia neurons by using an electrical field stimulation assay

Background

The Na_v1.7 subtype of voltage-gated sodium channels is specifically expressed in sensory and sympathetic ganglia neurons where it plays an important role in the generation and transmission of information related to pain sensation. Human loss or gain-of-function mutations in the gene encoding Na_v1.7 channels (SCN9A) are associated with either absence of pain, as reported for congenital insensitivity to pain, or with exacerbation of pain, as reported for primary erythromelalgia and paroxysmal extreme pain disorder. Based on this important human genetic evidence, numerous drug discovery efforts are ongoing in search for Nav1.7 blockers as a novel therapeutic strategy to treat pain conditions.

Results

We are reporting here a novel approach to study Na_v1.7 function in cultured rat sensory neurons. We used live cell imaging combined with electrical field stimulation to evoke and record action potential-driven calcium transients in the neurons. We have shown that the tarantula venom peptide Protoxin-II, a known Na_v1.7 subtype selective blocker, inhibited electrical field stimulation-evoked calcium responses in dorsal root ganglia neurons with an IC₅₀ of 72 nM, while it had no activity in embryonic hippocampal neurons. The results obtained in the live cell imaging assay were supported by patch-clamp studies as well as by quantitative PCR and Western blotting experiments that confirmed the presence of Na_v1.7 mRNA and protein in dorsal root ganglia but not in embryonic hippocampal neurons.

Conclusions

The findings presented here point to a selective effect of Protoxin-II in sensory neurons and helped to validate a new method for investigating and comparing Na_v1.7 pharmacology in sensory versus central nervous system neurons. This will help in the characterisation of the selectivity of novel Na_v1.7 modulators using native ion channels and will provide the basis for the development of higher throughput models for enabling pain-relevant phenotypic screening.

Impaired contractility of the circular striated urethral sphincter muscle may contribute to stress urinary incontinence in female zucker fatty rats

AIM

Obesity has been an independent risk factor for female stress urinary incontinence (SUI), the mechanism of this association remains unknown. The aim of this study is to validate the hypothesis that urethral dysfunction is a possible contributor to SUI in obese women.

METHODS

Ten Zucker Fatty (ZF) (ZUC-Leprfa 185) and 10 Zucker Lean (ZL) (ZUC-Leprfa 186) female rats at 12-week-old were used in this experiment. The urethral sphincter rings were harvested from the bladder neck through to the most proximal 2/3 regions. In the organ bath study, single pulses of electrical field stimulation (EFS) were applied. For the fatiguing stimulation, repeated multi-pulse EFS with 70 mA were applied at frequency of 5 Hz for 5 min. Caffeine-containing Krebs' solution was administrated to contract the urethra until the contraction began to reach a plateau for 10 min. We performed immunofluorescence staining of the urethra after the experiment was finished.

RESULTS

Compared to ZL controls, ZF rats had significantly impaired muscle contractile activity (MCA) (P < 0.05). Also, ZF rats presented early fatiguing of MCA and had a significantly greater percentage of MCA decline from baseline in the fatiguing test (37.7% vs 25.6%, P < 0.05). The plateau of maximal MCA induced by caffeine in ZF rats was significantly lower than ZL controls (0.22 vs 0.36, P < 0.05).

CONCLUSIONS

This novel study showed that obese female rats had significantly impaired contractile properties of striated urethral sphincter, suggesting urethral dysfunction could be an important contributor to SUI in obesity.

A simple laboratory exercise with rat isolated esophagus and stomach fundus to reveal functional differences between striated and smooth muscle cells

This study describes an undergraduate student laboratory activity using isolated preparations from rat gastrointestinal tissues that possess contractile profiles typically exhibited by striated and smooth muscle cells. While students are introduced to an ex vivo methodology, they can compare differences in trace experiments, twitch aspects, phasic and tonic properties, force-frequency relationships, and pharmacological responsiveness of esophageal (striated) and fundic (smooth muscle) segments. Muscle strips were subjected to electrical field stimulation (EFS) applied by platinum electrodes immersed in the physiological solution. The contractile profile of EFS responses varied between these two types of gut preparations. Atropine and tubocurarine revealed differential inhibitory influences in esophagus or fundus tissues; caffeine and procaine produced similar effects, i.e., potentiation and blockade of the EFS-induced contractile response in these tissues, respectively. Experimental results obtained during the activity helped the improvement of student learning about basic concepts previously discussed in theoretical lectures. To measure student learning with this laboratory exercise, a questionnaire was applied before and after the activity, and the number of expected correct answers, concerning the mechanisms of contraction in striated and smooth muscle, could be clearly evidenced.

The adipokine chemerin amplifies electrical field-stimulated contraction in the isolated rat superior mesenteric artery

The adipokine chemerin causes arterial contraction and is implicated in blood pressure regulation, especially in obese subjects with elevated levels of circulating chemerin. Because chemerin is expressed in the perivascular adipose tissue (PVAT) that surrounds the sympathetic innervation of the blood vessel, we tested the hypothesis that chemerin (endogenous and exogenous) amplifies the sympathetic nervous system in mediating electrical field-stimulated (EFS) contraction. The superior mesenteric artery, with or without PVAT and with endothelium and sympathetic nerve intact, was mounted into isolated tissue baths and used for isometric contraction and stimulation. Immunohistochemistry validated a robust expression of chemerin in the PVAT surrounding the superior mesenteric artery. EFS (0.3-20 Hz) caused a frequency-dependent contraction in isolated arteries that was reduced by the chemerin receptor ChemR23 antagonist CCX832 alone (100 nM; with, but not without, PVAT), but not by the inactive congener CCX826 (100 nM). Exogenous chemerin-9 (1 μM)-amplified EFS-induced contraction in arteries (with and without PVAT) was blocked by CCX832 and the α-adrenergic receptor antagonist prazosin. CCX832 did not directly inhibit, nor did chemerin directly amplify, norepinephrine-induced contraction. Whole mount immunohistochemical experiments support colocalization of ChemR23 with the sympathetic nerve marker tyrosine hydroxylase in superior mesenteric PVAT and, to a lesser extent, in arteries and veins. These studies support the idea that exogenous chemerin modifies sympathetic nerve-mediated contraction through ChemR23 and that ChemR23 may be endogenously activated. This is significant because of the well-appreciated role of the sympathetic nervous system in blood pressure control.

Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles

Purpose

Brimonidine is an imidazoline compound used for the treatment of glaucoma, but having very little effect on pupil diameter. Like para-aminoclonidine, most imidazoline compounds interact with postsynaptic α-adrenoceptors and cause pupil dilatation. Therefore, as part of an investigation of the mechanism of action of brimonidine on pupil diameter, the present study was initiated to measure, in vitro, the relative potency of brimonidine on the pre- and postsynaptic α-adrenoceptors of rabbit iris dilator muscle.

Methods

The contractile activity of brimonidine and its effect on twitch contraction evoked by electrical field stimulation were studied in isolated rabbit iris dilator muscles by isometric tension recording.

Results

Brimonidine significantly inhibited the twitch contraction of the dilator muscle caused by field stimulation, without affecting the response to exogenously applied phenylephrine. Compared to phenylephrine, brimonidine caused only a small contractile response with % maximum contraction values of <10%.

Conclusion

These results suggest that brimonidine may act on nerve endings to inhibit adrenergic neurotransmission with very little effect on postsynaptic α-adrenoceptors. This may indicate that brimonidine reduced the pupil diameter just a little, thus improving night vision.

Effect of type II diabetes on male rat bladder contractility

Type II diabetes is the most prevalent form of diabetes. One of the primary complications of diabetes that significantly affects quality of life is bladder dysfunction. Many studies on diabetic bladder dysfunction have been performed in models of type I diabetes; however, few have been performed in animal models of type II diabetes. Using the Zucker Diabetic Fatty (ZDF) rat model of type II diabetes, we examined the contractility and sensitivity of bladder smooth muscle in response to mediators of depolarization-induced contraction, muscarinic receptor-mediated contraction, ATP-induced contraction, and neurogenic contraction. Studies were performed at 16 and 27 wk of age to monitor the progression of diabetic bladder dysfunction. Voiding behavior was also quantified. The entire bladder walls of diabetic rats were hypertrophied compared with that of control rats. Contractility and sensitivity to carbachol and ATP were increased at 27 wk in bladder smooth muscle strips from diabetic rats, suggesting a compensated state of diabetic bladder dysfunction. Purinergic signaling was increased in response to exogenous ATP in bladders from diabetic animals; however, the purinergic component of neurogenic contractions was decreased. The purinergic component of neurogenic contraction was reduced by P2X receptor desensitization, but was unchanged by P2X receptor inhibition in diabetic rats. Residual and tetrodotoxin-resistant components of neurogenic contraction were increased in bladder strips from diabetic animals. Overall, our results suggest that in the male ZDF rat model, the bladder reaches the compensated stage of function by 27 wk and has increased responsiveness to ATP.

Cellular mechanisms of activity-dependent BDNF expression in primary sensory neurons

Brain-derived neurotrophic factor (BDNF) is abundantly expressed by both developing and adult rat visceral sensory neurons from the nodose ganglion (NG) in vivo and in vitro. We have previously shown that BDNF is released from neonatal NG neurons by activity and regulates dendritic development in their postsynaptic targets in the brainstem. The current study was carried out to examine the cellular and molecular mechanisms of activity-dependent BDNF expression in neonatal rat NG neurons, using our established in vitro model of neuronal activation by electrical field stimulation with patterns that mimic neuronal activity in vivo. We show that BDNF mRNA (transcript 4) increases over threefold in response to a 4-h tonic or bursting pattern delivered at the frequency of 6 Hz, which corresponds to the normal heart rate of a newborn rat. No significant increase in BDNF expression was observed following stimulation at 1 Hz. The latter effect suggests a frequency-dependent mechanism of regulated BDNF expression. In addition to BDNF transcript 4, which is known to be regulated by activity, transcript 1 also showed significant upregulation. The increases in BDNF mRNA were followed by BDNF protein upregulation of a similar magnitude after 24h of stimulation at 6 Hz. Electrical stimulation-evoked BDNF expression was inhibited by pretreating neurons with the blocker of voltage-gated sodium channels tetrodotoxin and by removing extracellular calcium. Moreover, our data show that repetitive stimulation-evoked BDNF expression requires calcium influx through N-, but not L-type, channels. Together, our study reveals novel mechanisms through which electrical activity stimulates de novo synthesis of BDNF in sensory neurons, and points to the role of N-type calcium channels in regulating BDNF expression in sensory neurons in response to repetitive stimulation.

Effects of (r,r)- and (r,r/s,s)-formoterol on airway relaxation and contraction in an experimental rat model

BACKGROUND

Racemic (R,R/S,S)-formoterol is a long-acting β-agonist composed of a 50:50 mixture of (R,R)- and (S,S)-enantiomers.

OBJECTIVE

The aim of this study was to determine whether (R,R)-formoterol and (R,R/S,S)-formoterol have differing effects on airway contraction and relaxation in vitro.

METHODS

Cylindrical airway segments 3-mm long were isolated from the mid-trachea of healthy Sprague-Dawley rats and placed in a modified Krebs-Henseleit solution. Dose-response curves of bethanechol-induced contraction (measured as milligrams of tension) and the concentration of bethanechol that elicited 50% to 75% of maximal contraction (EC50-75) were determined. The air-way cylinders were then precontracted with bethanechol at the EC50-75 and exposed to different concentrations of (R,R)-formoterol (0.0001-1.0 μM) or (R,R/S,S)-formoterol (0.0002-2.0 μM). Each concentration of the 2 formoterol formulations contained the same amount of (R,R)-enantiomer (eg, [R,R]-formoterol 0.0001 μM and [R,R/S,S]-formoterol 0.0002 1JM contained the same amount of [R,R]-enantiomer). The relaxation percentage in response to formoterol was calculated as a reduction in tension (in milligrams) in relation to baseline tension in the precontracted state, with each tracheal cylinder serving as its own control. To determine the effect of (R,R)-formoterol on airway contraction, tracheal cylinders were incubated with (R,R)- or (R,R/S,S)-formoterol before electrical field stimulation (EFS).

RESULTS

Tracheae from 56 three-week-old Sprague-Dawley rats were used in the study. The relaxation percentage of precontracted trachea was significantly greater after exposure to (R,R)-formoterol than to (R,R/S,S)-formoterol at a 2-fold higher concentration (P = 0.03; general linear model with repeated measures analysis comparing the 2 groups of animals). However, in a post hoc analysis, the mean (SE) relaxation percentage of precontracted trachea was significantly greater only after exposure to (R,R)-formoterol 0.01 μM than to (R,R/S,S)-formoterol 0.02 μM (15.6% [5.8%] vs 39.0% [5.6%]; P < 0.05, unpaired t test). EFS-induced airway contraction was significantly less in tracheal cylinders incubated in (R,R)-formoterol compared with those incubated in (R,R/S,S)-formoterol at a 2-fold higher concentration (P = 0.05; general linear model with repeated measures analysis comparing the 2 groups of animals). However, in the post hoc analysis, mean (SE) EFS-induced tracheal contraction was significantly less only in (R,R)-formoterol 0.01 μM compared with (R,R/S,S)-formoterol 0.02 μM at 10 V (1070 [55] mgvs 1225 [28] mg; P < 0.05, unpaired t test).

CONCLUSION

We found that (R,R)-formoterol may induce greater relaxation of precontracted airway smooth muscle cells than (R,R/S,S)-formoterol and that (R,R)-formoterol may have a greater inhibitory effect on the endogenous cholinergic and excitatory nonadrenergic, noncholinergic contractile airway responses than (R,R/S,S)-formoterol. We speculate that the presence of the (S,S)-enantiomer in (R,R/S,S)-formoterol may impair airway relaxation of pre-contracted trachea in rats.

Low-dose salbutamol suppresses airway responsiveness to histamine but not methacholine in subjects with asthma

BACKGROUND

Airway hyperresponsiveness is a cardinal feature of asthma. Although the modulation of cholinergic neuroeffector transmission may play a role in airway responsiveness, in vivo evidence remains scarce. It is well known that histamine causes bronchoconstriction partly via vagal reflex, whereas methacholine does not. To investigate the significance of modulating neuroeffector transmission, we compared the effect of low-dose salbutamol-a β2-adrenoceptor agonist-on airway responsiveness to histamine with that to methacholine.

METHODS

We enrolled 12 subjects with stable asthma. After screening confirmed that inhalation of low-dose salbutamol (1μg) did not change their basic pulmonary function, subjects underwent measurement of airway responsiveness to inhaled histamine and methacholine with or without pretreatment with low-dose salbutamol, in a randomized, crossover fashion. Airway responsiveness was measured by an astograph by which respiratory conductance (Grs) was assessed by the forced oscillation method during continuous inhalation of histamine or methacholine in stepwise incremental concentrations. Airway responsiveness was calculated as the cumulative dose of bronchoconstrictors that induced a decrease of 35% in Grs.

RESULTS

Inhalation of 1μg of salbutamol significantly attenuated airway responsiveness to histamine but not methacholine. This selective attenuation was observed irrespective of disease severity or phenotype, namely atopy or non-atopy.

CONCLUSION

Low-dose salbutamol suppresses airway responsiveness to histamine but not methacholine in subjects with asthma. The present study may provide a novel insight into the bronchoprotective mechanism of β2-adorenoceptor agonist in clinical settings.

Effect of wine polyphenol resveratrol on the contractions elicited electrically or by norepinephrine in the rat portal vein

We investigated the effects of resveratrol on rat portal vein (RPV) contractility without endothelium. Contractions were produced by electrical field stimulation of perivascular nerves (EFS), norepinephrine (NE), adenosine 5'-triphosphate (ATP), high K(+) solution and by calcium chloride (CaCl2 ) in Ca(2+) -free and high K(+) , Ca(2+) -free solution. The EFS-evoked contractions were more sensitive to resveratrol and to NS1619-selective openers of big calcium-sensitive (BKCa ) channels, than NE-evoked contractions. Effects of resveratrol on the ATP-evoked contractions were weak. Blockers of BKCa channels partly inhibited the effect of resveratrol only in EFS-contracted preparations. Western blotting showed that RPV expressed KCa 1.1 protein. Inhibitors of ATP- and voltage-sensitive K(+) channels did not modify the effects of resveratrol. None of the antagonists of K(+) channels affected the resveratrol inhibition of NE-evoked contractions and effect of high concentrations of resveratrol on the EFS-evoked contractions. Resveratrol more potently inhibited CaCl2 than potassium chloride contractions of RPV. Thus, BKCa channels partly mediate the inhibitory effect of resveratrol on the neurogenic contractions of RPV. The smooth muscle Ca(2+) channels and/or Ca(2+) mobilizing through cells might be involved in the effects of resveratrol on the contractility of RPV. Our results are important for better understanding the impact of resveratrol on the portal circulation.

A direct inhibitory effect of botulinum toxin type A on antral circular muscle contractility of guinea pig

PURPOSE

Recent studies suggest new mechanisms of Botulinum toxin (BoNT) other than inhibiting acetylcholine (ACh) release from nerve terminals. The aim of this study was to determine whether other mechanisms for BoNT exist, so that it directly inhibits smooth muscle contraction.

MATERIALS AND METHODS

Guinea pig antral muscle strips were studied in vitro after 2 hours of exposure to Botulinum toxin type A (BoNT/A). Contractile responses to electric field stimulation (EFS), high K(+) (60 mM) and ACh (100 μM) were evaluated 24 and 48 hours after antral intramuscular injection of BoNT/A or vehicle.

RESULTS

BoNT/A inhibited muscular contraction caused by high K(+) and ACh. Contractile responses to low (1 and 4 Hz) and high (8 and 20 Hz) frequency EFS of antral muscle strips 24 and 48 hours after antral intramuscular injection of BoNT/A were significantly inhibited.

CONCLUSION

The ability of BoNT/A to directly inhibit antral muscular contractility suggests a new mechanism for the pharmacologic actions of BoNT-direct inhibition of muscular contraction.

Role of carbon monoxide in electrically induced non-adrenergic, non-cholinergic relaxations in the guinea-pig isolated whole trachea

BACKGROUND AND PURPOSE

Nitric oxide (NO) and vasoactive intestinal peptide (VIP) are considered transmitters of non-adrenergic, non-cholinergic (NANC) relaxations in guinea-pig trachea, whereas the role of carbon monoxide (CO) is unknown. This study was designed to assess the participation of CO, and to investigate the localization of haem oxygenase-2 (HO-2), the CO-producing enzyme, in tracheal neurons.

EXPERIMENTAL APPROACH

NANC responses to electrical field stimulation (EFS) at 3 and 10 Hz were evaluated in epithelium-free whole tracheal segments as intraluminal pressure changes. Drugs used were: L-nitroarginine methyl ester (L-NAME, 100 microM) to inhibit NO synthase (NOS), alpha-chymotrypsin (2 U ml(-1)) to inactivate VIP, zinc protoporphyrin-IX (ZnPP-IX, 10 microM) to inhibit HO-2, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), a soluble guanylyl cyclase inhibitor. For immunohistochemistry, tissues were exposed to antibodies to PGP 9.5, a general neuronal marker, HO-2 and NOS, and processed with an indirect immunofluorescence method.

KEY RESULTS

alpha-Chymotrypsin did not affect NANC relaxations. ODQ inhibited NANC responses by about 60%, a value similar to that obtained by combining L-NAME and ZnPP-IX. The combination of ODQ, L-NAME and ZnPP-IX reduced the responses by 90%. Subpopulations of HO-2 positive neurons containing NOS were detected in tracheal sections.

CONCLUSIONS AND IMPLICATIONS

In the guinea-pig trachea, NANC inhibitory responses at 3 and 10 Hz use NO and CO as main transmitters. Their participation is revealed following inhibition of NOS, HO-2 and soluble guanylyl cyclase. The involvement of CO as a relaxing transmitter paves the way for novel therapeutic approaches in the treatment of airway obstruction.

Gastric motor effects of peptide and non-peptide ghrelin agonists in mice in vivo and in vitro

BACKGROUND AND AIMS

The gastroprokinetic activities of ghrelin, the natural ligand of the growth hormone secretagogue receptor (GHS-R), prompted us to compare the effect of ghrelin with that of synthetic peptide (growth hormone releasing peptide 6 (GHRP-6)) and non-peptide (capromorelin) GHS-R agonists both in vivo and in vitro.

METHODS

In vivo, the dose dependent effects (1-150 nmol/kg) of ghrelin, GHRP-6, and capromorelin on gastric emptying were measured by the 14C octanoic breath test which was adapted for use in mice. The effect of atropine, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME), or D-Lys3-GHRP-6 (GHS-R antagonist) on the gastroprokinetic effect of capromorelin was also investigated. In vitro, the effect of the GHS-R agonists (1 microM) on electrical field stimulation (EFS) induced responses was studied in fundic strips in the absence and presence of L-NAME.

RESULTS

Ghrelin, GHRP-6, and capromorelin accelerated gastric emptying in an equipotent manner, with bell-shaped dose-response relationships. In the presence of atropine or l-NAME, which delayed gastric emptying, capromorelin failed to accelerate gastric emptying. D-Lys3-GHRP-6 also delayed gastric emptying but did not effectively block the action of the GHS-R agonists, but this may be related to interactions with other receptors. EFS of fundic strips caused frequency dependent relaxations that were not modified by the GHS-R agonists. L-NAME turned EFS induced relaxations into cholinergic contractions that were enhanced by ghrelin, GHRP-6, and capromorelin.

CONCLUSION

The 14C octanoic breath test is a valuable technique to evaluate drug induced effects on gastric emptying in mice. Peptide and non-peptide GHS-R agonists accelerate gastric emptying of solids in an equipotent manner through activation of GHS receptors, possibly located on local cholinergic enteric nerves.

Alpha1-adrenoceptor subtypes involved in vasoconstrictor responses to exogenous and neurally released noradrenaline in rat femoral resistance arteries

1. The alpha(1)-adrenoceptor subtypes involved in responses to exogenous and neurally released noradrenaline in rat femoral resistance arteries were characterised using a small vessel myograph, with antagonists prazosin (nonsubtype selective), 5-methyl-urapidil (alpha(1A)-selective), BMY 7378 (alpha(1D)-selective) and the alkylating agent chloroethylclonidine (preferential for alpha(1B)-). 2. Prazosin and 5-methyl-urapidil produced rightward shifts of the exogenous noradrenaline concentration - response curve (CRC) with pA(2) values of 9.2 and 9.1 respectively, in agreement with the presence of alpha(1A)-adrenoceptors. BMY 7378 (1 microm) shifted the noradrenaline CRC with an apparent pK(B) of 6.7, in agreement with the presence of alpha(1A)-, but not alpha(1D)-, adrenoceptors. Chloroethylclonidine at 1 microm had no effect and at 10 microm produced only a small reduction (c. 20%) in the maximum response to noradrenaline, indicating little, if any, contribution from alpha(1B)-adrenoceptors. 3. Responses of the rat femoral resistance arteries to electrical field stimulation (EFS) at 5-30 Hz for 10 s and 0.05 ms pulse width were principally due to alpha(1)-adrenoceptor stimulation. Prazosin and 5-methyl-urapidil inhibited EFS-mediated responses with pIC(50)s of 9.3 and 8.2, respectively, consistent with the alpha(1A)-adrenoceptor being the predominant subtype. Responses to EFS at 10-30 Hz were relatively insensitive to BMY 7378 (pIC(50), 6.5-6.7), while responses to 5 Hz were inhibited with a significantly higher pIC(50) of 8.02, suggesting the contribution of alpha(1D)-adrenoceptors. Chloroethylclonidine had no effect on responses to EFS, ruling out the contribution of an alpha(1B)-subtype. In the presence of cocaine, the predominant subtype involved in responses to EFS was the alpha(1A)-adrenoceptor, with a contribution from alpha(1D)-adrenoceptors at low frequency, as seen in the absence of cocaine. However, there was also a significant increase in the sensitivity to BMY 7378 at higher frequencies, suggesting that a further small alpha(1D)-adrenoceptor component may be uncovered in the presence of cocaine. 5. The present study has shown a predominant role of the alpha(1A)-adrenoceptor in contractions due to exogenous noradrenaline and to neurally released noradrenaline in rat femoral resistance arteries. alpha(1D)-Adrenoceptors are not involved in responses to exogenous noradrenaline but appear to be activated by neurally released noradrenaline at a low frequency of stimulation and at higher frequencies in the presence of neuronal-uptake blockade.

Cellular mechanisms regulating activity-dependent release of native brain-derived neurotrophic factor from hippocampal neurons

Brain-derived neurotrophic factor (BDNF) plays a critical role in activity-dependent modifications of neuronal connectivity and synaptic strength, including establishment of hippocampal long-term potentiation (LTP). To shed light on mechanisms underlying BDNF-dependent synaptic plasticity, the present study was undertaken to characterize release of native BDNF from newborn rat hippocampal neurons in response to physiologically relevant patterns of electrical field stimulation in culture, including tonic stimulation at 5 Hz, bursting stimulation at 25 and 100 Hz, and theta-burst stimulation (TBS). Release was measured using the ELISA in situ technique, developed in our laboratory to quantify secretion of native BDNF without the need to first overexpress the protein to nonphysiological levels. Each stimulation protocol resulted in a significant increase in BDNF release that was tetrodotoxin sensitive and occurred in the absence of glutamate receptor activation. However, 100 Hz tetanus and TBS, stimulus patterns that are most effective in inducing hippocampal LTP, were significantly more effective in releasing native BDNF than lower-frequency stimulation. For all stimulation protocols tested, removal of extracellular calcium, or blockade of N-type calcium channels, prevented BDNF release. Similarly, depletion of intracellular calcium stores with thapsigargin and treatment with dantrolene, an inhibitor of calcium release from caffeine-ryanodine-sensitive stores, markedly inhibited activity-dependent BDNF release. Our results indicate that BDNF release can encode temporal features of hippocampal neuronal activity. The dual requirement for calcium influx through N-type calcium channels and calcium mobilization from intracellular stores strongly implicates a role for calcium-induced calcium release in activity-dependent BDNF secretion.

Generalized loss of inhibitory innervation reverses serotonergic inhibition into excitation in a rabbit model of TNBS-colitis

1. Inflammation may affect subpopulations of neurons of the myenteric plexus. 2. In the present study the effect of trinitrobenzene sulphonic acid (TNBS) induced colitis on nitrergic, purinergic and adrenergic inhibitory neurotransmission was studied as well as the consequences of the related changes on the response of 5-HT agonists using these neurotransmitters to mediate their effect. 3. Strips from normal and colitis rabbits (135 mg kg(-1) TNBS) were subjected to electrical field stimulation (EFS, 0.3 ms, 6V, 0.5 - 32 Hz, 10 s train). The response was measured isometrically in the absence or presence of L-NAME, suramin, guanethidine, the 5-HT agonists (5-HT(1/5A/7): 5-carboxamidotryptamine (5-CT), 5-HT(2): alpha-methyl-5-HT, 5-HT(3): 2-methyl-5-HT, 5-HT(4): 5-methoxytryptamine (5-MeOT)) or a combination. 4. In normal strips L-NAME (1 - 32 Hz), suramin (0.5 - 2, 8 Hz) and guanethidine (4, 16, 32 Hz) increased the response to EFS. This effect was abolished in inflamed strips and was accompanied by a decrease in nNOS expression. 5. In normal strips all 5-HT agonists induced pronounced (5-CT, alpha-methyl-5-HT) or small (2-methyl-5-HT, 5-MeOT) inhibitory neural responses. In inflamed strips this was reversed to cholinergic excitatory responses. 6. The effect of inflammation on the 5-HT(4) response was mimicked by preincubation of normal strips with L-NAME or suramin. Accordingly, in inflamed strips L-NAME or suramin did not affect the excitatory effects of 5-MeOT. 7. TNBS-colitis abolishes nitrergic, purinergic and adrenergic neurotransmission. This reverses serotonergic inhibition into excitation.

Activity-dependent release of endogenous brain-derived neurotrophic factor from primary sensory neurons detected by ELISA in situ

To define activity-dependent release of endogenous brain-derived neurotrophic factor (BDNF), we developed an in vitro model using primary sensory neurons and a modified ELISA, termed ELISA in situ. Dissociate cultures of nodose-petrosal ganglion cells from newborn rats were grown in wells precoated with anti-BDNF antibody to capture released BDNF, which was subsequently detected using conventional ELISA. Conventional ELISA alone was unable to detect any increase in BDNF concentration above control values following chronic depolarization with 40 mM KCl for 72 hr. However, ELISA in situ demonstrated a highly significant increase in BDNF release, from 65 pg/ml in control to 228 pg/ml in KCl-treated cultures. The efficacy of the in situ assay appears to be related primarily to rapid capture of released BDNF that prevents BDNF binding to the cultured cells. We therefore used this approach to compare BDNF release from cultures exposed for 30 min to either continuous depolarization with elevated KCl or patterned electrical field stimulation (50 biphasic rectangular pulses of 25 msec, at 20 Hz, every 5 sec). Short-term KCl depolarization was completely ineffective at evoking any detectable release of BDNF, whereas patterned electrical stimulation increased extracellular BDNF levels by 20-fold. In addition, the magnitude of BDNF release was dependent on stimulus pattern, with high-frequency bursts being most effective. These data indicate that the optimal stimulus profile for BDNF release resembles that of other neuroactive peptides. Moreover, our findings demonstrate that BDNF release can encode temporal features of presynaptic neuronal activity.

Influence of gender and the oestrous cycle on in vitro contractile responses of the rat urinary bladder to cholinergic stimulation

1. Experiments were done to determine the influence of gender and the oestrous cycle on rat urinary bladder contractility in response to cholinergic stimulation. 2. Bladder strips from female rats responded to high frequency stimulation with smaller contractile responses than did strips from males, and to low concentrations of carbachol with greater responses. The decreased responsiveness of bladder strips from female rats to electrical field stimulation can be primarily attributed to the rats in the oestrous stage of the oestrous cycle. 3. Bladder strips from female rats in all stages of the oestrous cycle were more sensitive to carbachol than those from males, but there were no differences in sensitivity to electrical field stimulation. 4. The contractile responses of strips from both male and female rats to carbachol were antagonized by muscarinic antagonists with the following rank order of affinity (pA(2)) estimates: 4-DAMP>>pirenzepine>methoctramine, suggesting that the receptor mediating contraction was the M3 subtype. There were no differences in pA(2) values between bladder strips from male and female rats. 5. The data indicate that responsiveness of bladder strips to electrical field stimulation and carbachol is altered in female rats in the oestrous stage of the oestrous cycle. Furthermore, gender influences the sensitivity of rat bladder to muscarinic stimulation.

A2B adenosine receptors mediate relaxation of the pig intravesical ureter: adenosine modulation of non adrenergic non cholinergic excitatory neurotransmission

1. The present study was designed to characterize the adenosine receptors involved in the relaxation of the pig intravesical ureter, and to investigate the action of adenosine on the non adrenergic non cholinergic (NANC) excitatory ureteral neurotransmission. 2. In U46619 (10(-7) M)-contracted strips treated with the adenosine uptake inhibitor, nitrobenzylthioinosine (NBTI, 10(-6) M), adenosine and related analogues induced relaxations with the following potency order: 5'-N-ethylcarboxamidoadenosine (NECA) = 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA) = 2-chloroadenosine (2-CA) > adenosine > cyclopentyladenosine (CPA) = N6-(3-iodobenzyl)-adenosine-5'-N-methylcarboxamide (IB-MECA) = 2-[p-(carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoaden os ine (CGS21680). 3. Epithelium removal or incubation with indomethacin (3 x 10(-6) M) and L-N(G)-nitroarginine (L-NOARG, 3 x 10(-5) M), inhibitors of prostanoids and nitric oxide (NO) synthase, respectively, failed to modify the relaxations to adenosine. 4. 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10(-8) M) and 4-(2-[7-amino-2-(2-furyl) [1,2,4]-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385, 3 x 10(-8) M and 10(-7) M), A1 and A2A receptor selective antagonists, respectively, did not modify the relaxations to adenosine or NECA. 8-phenyltheophylline (8-PT, 10(-5) M) and DPCPX (10(-6) M), which block A1/A2-receptors, reduced such relaxations. 5. In strips treated with guanethidine (10(-5) M), atropine (10(-7) M), L-NOARG (3 x 10(-5) M) and indomethacin (3 x 10(-6) M), both electrical field stimulation (EFS, 5 Hz) and exogenous ATP (10(-4) M) induced contractions of preparations. 8-PT (10(-5) M) increased both contractions. DPCPX (10(-8) M), NECA (10(-4) M), CPCA, (10(-4) M) and 2-CA (10(-4) M) did not alter the contractions to EFS. 6. The present results suggest that adenosine relaxes the pig intravesical ureter, independently of prostanoids or NO, through activation of A2B-receptors located in the smooth muscle. This relaxation may modulate the ureteral NANC excitatory neurotransmission through a postsynaptic mechanism.

Pharmacological characterization of thromboxane and prostanoid receptors in human isolated urinary bladder

1. Cumulative concentration-response curves (CRC) to prostaglandin E1 (PGE1), PGE2, PGD2 and PGF2alpha (0.01-30 microM) and to the thromboxane A2 (TXA2) receptor agonist U-46619 (0.01-30 microM) were constructed in human isolated detrusor muscle strips both in basal conditions and during electrical field stimulation. 2. All the agonists tested contracted the detrusor muscle. The rank order of agonist potency was: PGF2alpha > U-46619 > PGE2 whereas weak contractile responses were obtained with PGD2 and PGE1. Any of the agonists tested was able to induce a clear plateau of response even at 30 microM. 3. The selective TXA2 antagonist, GR 32191B (vapiprost), antagonized U-46619-induced contractions with an apparent pK(B) value of 8.27+/-0.12 (n = 4 for each antagonist concentration). GR 32191B (0.3 microM) did not antagonize the contractile responses to PGF2alpha and it was a non-surmountable antagonist of PGE2 (apparent pK(B) of 7.09+/-0.04; n = 5). The EP receptor antagonist AH 6809 at 10 microM shifted to the right the CRC to U-46619 (apparent pK(B) value of 5.88+/-0.04; n = 4). 4. Electrical field stimulation (20 Hz, 70 V, pulse width 0.1 ms, trains of 5 s every 60 s) elicited contractions fully sensitive to TTX (0.3 microM) and atropine (1 microM). U-46619 (0.01-3 microM) potentiated the twitch contraction in a dose-dependent manner and this effect was competitively antagonized by GR 32191B with an estimated pK(B) of 8.54+/-0.14 (n = 4 for each antagonist concentration). PGF2alpha in the range 0.01-10 microM (n = 7), but not PGE2 and PGE1 (n = 3 for each), also potentiated the twitch contraction of detrusor muscle strips (23.5+/-0.3% of KCl 100 mM-induced contraction) but this potentiation was unaffected by 0.3 microM GR 32191B (n = 5). 5. Cumulative additions of U-46619 (0.01-30 microM) were without effect on contractions induced by direct smooth muscle excitation (20 Hz, 40 V, 6 ms pulse width, trains of 2 s every 60 s, in the presence of TTX 1 microM; n = 3). Moreover, pretreatment of the tissue with 0.3 microM U-46619 did not potentiate the smooth muscle response to 7 microM bethanecol (n = 2). 6. We concluded that TXA2 can induce direct contraction of human isolated urinary bladder through the classical TXA2 receptor. Prostanoid receptors, fully activated by PGE2 and PGF2alpha are also present. All these receptors are probably located post-junctionally. The rank order of agonist potency and the fact that GR 32191B, but not AH6809, antagonized responses to PGE2 seem to indicate the presence of a new EP receptor subtype. Moreover, we suggest the presence of prejunctional TXA2 and FP receptors, potentiating acetylcholine release from cholinergic nerve terminals.

Effect of clenbuterol on non-endothelial nitric oxide release in rat mesenteric arteries and the involvement of beta-adrenoceptors

1. The aim of the present study was to explore the contribution of adrenergic, sensory and nitrergic innervations to the inhibitory effects of the beta2-adrenoceptor agonist clenbuterol on responses to electrical field stimulation (EFS, 200 mA, 0.3 ms, 1-16 Hz, for 30 s, at 1 min interval) in rat mesenteric artery segments without endothelium and the possible involvement of adrenergic, sensory and nitrergic innervations. 2. Clenbuterol (1 microM) reduced EFS-induced contractile responses, and this effect was reversed by the beta-antagonist propranolol (1 microM) (contraction at 16 Hz expressed as % of 75 mM K+-induced contraction was: control, 69+/-9, clenbuterol, 31+/-6, n=13, P<0.001; control, 83+/-5, clenbuterol+propranolol 70+/-7, n=11, P>0.05). 3. In arteries preincubated with [3H]-noradrenaline (NA), clenbuterol did not modify the tritium overflow evoked by EFS (200 mA, 0.3 ms, 4 Hz, for 60 s; ratio between tritium release in the second and first stimuli was: control, 0.80+/-0.05 and clenbuterol added before second stimulus, 0.91+/-0.11, n=5, P>0.05). 4. The nitric oxide (NO) synthase inhibitors NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) (10 and 100 microM), and the guanylate cyclase inhibitor methylene blue (10 microM) increased the contractions caused by EFS (% contraction at 16 Hz, control, 81+/-7, n=26; 10 microM L-NMMA, 109+/-12, n=8, P<0.05; methylene blue, 119+/-6, n=6, P<0.05). However, these contractions were decreased by the NO synthase substrate L-arginine 10 microM (14+/-6%, n=6, P<0.001), but not modified by either the sensory neurones toxin capsaicin (0.5 microM, 75+/-6%, n=6, P>0.05) or the protein synthesis inhibitor cycloheximide (10 microM, 83+/-6%, n=8, P>0.05). None of these drugs altered the concentration-response curves to exogenous NA (n=7). 5. Pretreatment with capsaicin or cycloheximide did not modify the reduction of the EFS-evoked contraction provoked by clenbuterol. However the presence of L-NMMA (or L-NAME) or methylene blue did decrease the effect of clenbuterol (% contraction at 16 Hz, clenbuterol, 31+/-6, n=13; clenbuterol+10 microM L-NMMA, 93+/-11, n=8, P<0.05; clenbuterol+methylene blue, 90+/-7, n=6, P<0.05). 6. These results suggest that the reduction caused by clenbuterol in the contraction induced by EFS in rat mesenteric arteries seems to be mediated by NO release, through the activation of beta2-adrenoceptors probably present on nitrergic nerves.

The relevance of resting tension to responsiveness and inherent tone of human bronchial smooth muscle

1. In the present study the effects of resting tension on isometric responses of human airway smooth muscle to contractile and relaxant stimuli were investigated. Also, its effects on inherent smooth muscle tone were examined, in an effort to determine a pre-defined resting tension which can be considered optimal for in vitro studies. 2. Bronchial ring preparations (2-4 mm internal diameter) were suspended in tissue baths at a range of levels of resting tension (200-1600 mg). The responses to electrical field stimulation (EFS, 30 V, 0.2 ms, 8-30 Hz), carbachol (3 microM), isoprenaline (1 microM) and the 5-lipoxygenase inhibitor, zileuton (10 microM) were investigated along with the ability of the preparations to recover stable resting tension after 60 min of washing post challenge. 3. EFS induced monophasic contractions at low stimulation frequency (8 Hz). However, with increasing frequency and tension (15 and 30 Hz; > 400 mg) contractile responses were accompanied by a relaxant component. The magnitude of contractile responses increased with increasing resting tension to a plateau at between 500 and 700 mg. Relaxant responses when present, increased in magnitude with increasing resting tension. 4. The level of resting tension did not significantly alter responses to carbachol, but tissues at tensions > or = 1000 mg showed poor tension recovery after washing. Isoprenaline-induced relaxations increased with increasing resting tension (P<0.05) and tension recovery after washing was complete. The 5-lipoxygenase sensitive portion of the tension (33+/-4%) was not altered by the level of resting tension. 5 These results suggest that in human bronchial ring preparations of 2-4 mm internal diameter, resting tensions within the range 400-1000 mg could be considered optimal for isometric tension recordings of protocols involving both contraction and relaxation procedures.

Action of ryanodine on neurogenic responses in rat isolated mesenteric small arteries

1. Rat mesenteric (approximately 250 microns) were set up in a single-channel isometric myograph designed to allow with 6 microM fura-2AM for 2 h and simultaneous recordings of neurogenic contraction (force) and intracellular calcium [Ca2+]i were obtained. In other experiments, arteries were loaded with 1 microCi ml-1 [3H]-noradrenaline (NA) for 30 min in order to measure release of [3H]-NA in response to field stimulation to examine whether ryanodine directly inhibited neuronal release of NA. 2. Arteries were activated by single intermittent field stimulation or continuously to excite intrinsic sympathetic nerves, or by cumulative addition of noradrenaline (1 nM-10 microM) to the bathing solution. 3. Pre-incubation with ryanodine markedly inhibited the contraction and [Ca2+]i release in response to single-pulse nerve stimulation. Ryanodine also inhibited an early phasic component of the response to continuous field stimulation and reduced the rate of rise in force in response to continuous field stimulation. However, stable maximal contraction and [Ca2+]i in response to continuous field stimulation as well as maximal responses to exogenous NA were unaffected. Release of [3H]-NA in response to single intermittent field stimulation was not affected by ryanodine when compared to vehicle. 4. Our results suggest that brief intermittent activation of intramural sympathetic nerves increases [Ca2+]i and contracts small arteries primarily by releasing Ca2+ from a ryanodine-sensitive intracellular store. In contrast, the stable rise in tone and [Ca2+]i resulting from continuous nerve stimulation may largely depend on sources of Ca2+ other than the ryanodine-sensitive intracellular store.

Involvement of a glibenclamide-sensitive mechanism in the nitrergic neurotransmission of the pig intravesical ureter

1. The present study was designed to investigate whether potassium (K+) channels are involved in the relaxations to nitric oxide (NO) of pig intravesical ureteral preparations suspended in organ baths for isometric tension recordings. In ureteral strips treated with guanethidine (10(-5) M) and atropine (10(-7) M) to block adrenergic neurotransmission and muscarinic receptors, respectively, NO was either released from nitrergic nerves by electrical field stimulation (EFS, 0.5-10 Hz., 1 ms duration, 20 s trains), or exogenously-applied as an acidified solution of sodium nitrite (NaNO2, 10(-6)-10(-3) M). 2. Incubation with an inhibitor of guanylate cyclase activation by NO, methylene blue (10(-5) M) did not change the basal tension of intravesical ureteral strips but inhibited the relaxation induced by EFS or exogenous NO on ureteral preparations contracted with the thromboxane analogue U46619 (10(-7) M). 3. Incubation with charybdotoxin (3 x 10(-8) M) and apamin (5 x 10(-7) M), which are inhibitors of large and small conductance calcium (Ca2+)-activated K+ channels, respectively, did not modify basal tension or the relaxations induced by EFS and exogenous NO. Treatment with charybdotoxin or apamin plus methylene blue (10(-5) M) significantly reduced the relaxations to EFS and exogenous NO. However, in both cases the reductions were similar to the inhibition evoked by methylene blue alone. The combined addition of charybdotoxin plus apamin did not change the relaxations to EFS or exogenously added NO of the porcine intravesical ureter. 4. Cromakalim (10(-8) 3 x 10(-6) M), an opener of ATP-sensitive K+ channels, evoked a dose-dependent relaxation with a pD2 of 7.3 +/- 0.2 and maximum relaxant effect of a 71.8 +/- 4.2% of the contraction induced by U46619 in the pig intravesical ureter. The blocker of ATP-sensitive K+ channels, glibenclamide (10(-6) M), inhibited markedly the relaxations to cromakalim. 5. Glibenclamide (10(-6) M) had no effect on the basal tone of ureteral preparations but significantly reduced the relaxations induced by both EFS and exogenous NO. Combined treatment with methylene blue (10(-5) M) and glibenclamide (10(-6) M) did not exert an effect greater than that of methylene blue alone on either EFS- or NO-evoked relaxations of the pig ureter. 6. The present results suggest that NO acts as an inhibitory neurotransmitter in the pig intravesical ureter and relaxes smooth muscle through a guanylate cyclase-dependent mechanism which seems to favour the opening of glibenclamide-sensitive K+ channels.

Involvement of ATP in the non-adrenergic non-cholinergic inhibitory neurotransmission of lamb isolated coronary small arteries

1. The involvement of non-adrenergic non-cholinergic (NANC) transmitters, such as nitric oxide (NO) and adenosine 5'-triphosphate (ATP), in the neurogenic relaxation of lamb coronary small arteries was investigated in vessel segments with an internal lumen diameter of 200-550 microns, isolated from the left ventricle of the heart, and suspended for isometric tension recording in microvascular myographs. 2. In both endothelium-intact and -denuded coronary small arteries treated with phentolamine (3 x 10(-6) M), propranolol (3 x 10(-6) M), and atropine (10(-6) M) and contracted to 3 x 10(-7) M of the thromboxane analogue U46619, electrical field stimulation (EFS) evoked frequency-dependent relaxations, which were markedly reduced in the presence of tetrodotoxin (10(-6) M). 3. Exogenous NO added as acidified sodium nitrite (10(-6)-10(-3) M) and L-nitrosocysteine induced potent relaxations of lamb coronary small arteries. However, both inhibition of NO synthase with NG- nitro-L-arginine (L-NOARG, 3 x 10(-5) M), and mechanical endothelial cell removal increased rather than inhibited relaxations to EFS. In small arteries processed for NADPH-diaphorase histochemistry, activity was only observed within endothelial cells. 4. In arteries contracted to U46619, exogenously added ATP caused concentration-dependent relaxations with pD2 and maximum responses of 4.72 +/- 0.12 and 89.6 +/- 3.8% (n = 12), respectively. ADP and the P2Y-agonist, 2-methylthio-ATP, induced relaxations equipotent to ATP, while the P2x-agonist, alpha, beta-methylene ATP (10(-9)-10(-4) M), and the P2U-agonist, UTP (10(-9)-10(-4) M) only caused small transient relaxations at the highest concentrations (10(-4) and 10(-3) M). 5. ATP and EFS-induced relaxations were unchanged in the presence of the P1-purinoceptor antagonist, 8-phenyltheophylline (10(-5) M), while this antagonist inhibited the concentration-dependent relaxations to adenosine. In contrast, the P2-purinoceptor antagonist, suramin (3 x 10(-5) M), markedly reduced the relaxations to EFS. 6. After desensitization of P2x-purinoceptors with alpha, beta-methylene ATP (2 x 10(-5) M), the relaxations to exogenous added ATP were enhanced, but this procedure did not influence the relaxations to EFS. In contrast, the P2y-purinoceptor antagonist, basilen blue E-3G (3 x 10(-5) M, earlier named reactive blue 2) significantly inhibited the concentration-relaxation curves to ATP and almost abolished the EFS-induced relaxations. 7. Mechanical removal of the endothelium significantly inhibited ATP-induced maximal relaxations without affecting sensitivity, pD2 and maximum relaxations being 4.72 +/- 0.12 and 89.7 +/- 3.8% (n = 10), and 5.45 +/- 0.38 and 48.0 +/- 8.6% (P < 0.05, paired t test, n = 10) in endothelium-intact and -denuded coronary small arteries, respectively. However, incubation with L-NOARG did not change relaxations elicited by ATP. 8. The present study suggests that in NANC conditions neurogenic relaxations of coronary small arteries are mediated by ATP, which relaxes coronary small arteries through P2Y-purinoceptors. A prejunctional modulation of these relaxations by endothelial-derived NO cannot be excluded.